Nocardiosis: Technical Information

Clinical Features

Overall, 80% of nocardiosis cases present as invasive pulmonary infection, disseminated infection, or brain abscess; 20% present as cellulitis. Pulmonary infection commonly presents with fever, cough, or chest pain. Central nervous system (CNS) symptoms include headache, lethargy, confusion, seizures, or sudden onset of neurologic deficit.

Etiologic Agent

The majority of cases are caused by the Nocardia asteroides complex (at least 50% of invasive infections). The N. asteroides complex is comprised of N. abscessus, N. cyriacigeorgica, N. farcinica, and N. nova. Other known pathogenic species of Nocardia include N. transvalensis complex, N. brasiliensis, and N. pseudobrasiliensis.

Incidence

In the United States, it has been estimated that 500-1,000 new cases of Nocardia infection occur annually. Approximately 60% of nocardiosis cases are associated with pre-existing immune compromise.

Sequelae

Approximately 10% of cases with uncomplicated pneumonia are fatal. The case-fatality rate increases with overwhelming infection, disseminated disease, or brain abscess. Surgical drainage may be indicated and may improve patient outcome.

Transmission

Pulmonary, disseminated and CNS infections are acquired through inhalation; primary cutaneous disease is acquired through inoculation of the skin. Rarely, nosocomial postsurgical transmission occurs.

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Risk Groups

Severely immunocompromised persons are at greatest risk for nocardiosis. These include persons with connective tissue disorders, malignancy, HIV infection, pulmonary alveolar proteinosis, alcoholism, or high-dose corticosteroid use.

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Surveillance

Nocardiosis is not a reportable condition.

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Trends

Although incidence data are extremely limited, the number of cases is likely rising as a result of the increase in the number of severely immunocompromised persons.

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Challenges

Diagnosis may be difficult. In the clinical laboratory, routine cultures may be held for insufficient time to grow Nocardiae, and referral to a reference laboratory may be needed for species identification. N. farcinica is more often resistant to antimicrobial agents, including trimethoprim-sulfamethoxazole (TMP-SMX), and has been shown to be more virulent in an animal model. TMP-SMX therapy for HIV-infected patients may be complicated by frequent occurrence of side effects and drug resistance.

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Opportunities

A new combination drug therapy (sulfonamide, ceftriaxone, and amikacin) has shown promise for treatment of infections not responding to standard antimicrobial treatments. Application of newer molecular diagnostic and subtyping methods may assist in earlier diagnosis.

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